Cerebral perfusion pressure and intracranial pressure are not surrogates for brain tissue oxygenation in traumatic brain injury

Brain tissue oxygen pressure combined with intracranial pressure monitoring may improve clinical outcomes for patients with severe traumatic brain injury: a systemic review and meta-analysis

Background

Although the optimization of brain oxygenation is thought to improve the prognosis, the effect of brain tissue oxygen pressure (PbtO2) for patients with severe traumatic brain injury (STBI) remains controversial. Therefore, the present study aimed to determine whether adding PbtO2 to intracranial pressure (ICP) monitoring improves clinical outcomes for patients with STBI.

Methods

PubMed, Embase, Scopus and Cochrane Library were searched for eligible trials from their respective inception through April 10th, 2024. We included clinical trials contrasting the combined monitoring of PbtO2 and ICP versus isolated ICP monitoring among patients with STBI. The primary outcome was favorable neurological outcome at 6 months, and secondary outcomes including the in-hospital mortality, long-term mortality, length of stay in intensive care unit (ICU) and hospital.

Results

A total of 16 studies (four randomized studies and 12 cohort studies) were included in the meta-analysis. Compared with isolated ICP monitoring, the combined monitoring was associated with a higher favorable neurological outcome rate at 6 months (RR 1.33, 95% CI [1.17-1.51], P < 0.0001, I2 = 0%), reduced long-term mortality (RR 0.72, 95% CI [0.59-0.87], P = 0.0008, I2 = 2%). No significant difference was identified in the in-hospital mortality (RR 0.81, 95% CI 0.66 to 1.01, P = 0.06, I2 = 32%), length of stay in ICU (MD 2.10, 95% CI [-0.37-4.56], P = 0.10, I2 = 78%) and hospital (MD 1.07, 95% CI [-2.54-4.67], P = 0.56, I2 = 49%) between two groups. However, the pooled results of randomized studies did not show beneficial effect of combined monitoring in favorable neurological outcome and long-term mortality.

Conclusions

Currently, there is limited evidence to prove that the combined PbtO2 and ICP monitoring may contribute to improved neurological outcome and long-term mortality for patients with STBI. However, the benefit of combined monitoring should be further validated in more randomized studies.

Brain tissue oxygen monitoring in moderate-to-severe traumatic brain injury: Physiological determinants, clinical interventions and current randomised controlled trial evidence

Modern intensive care for moderate-to-severe traumatic brain injury (msTBI) focuses on managing intracranial pressure (ICP) and cerebral perfusion pressure (CPP). This approach lacks robust clinical evidence and often overlooks the impact of hypoxic injuries. Emerging monitoring modalities, particularly those capable of measuring brain tissue oxygen, represent a promising avenue for advanced neuromonitoring. Among these, brain tissue oxygen tension (PbtO2) shows the most promising results. However, there is still a lack of consensus regarding the interpretation of PbtO2 in clinical practice. This review aims to provide an overview of the pathophysiological rationales, monitoring technology, physiological determinants, and recent clinical trial evidence for PbtO2 monitoring in the management of msTBI.

Intracranial pressure-flow relationships in traumatic brain injury patients expose gaps in the tenets of models and pressure-oriented management

Background: The protocols and therapeutic guidance established for treating traumatic brain injury (TBI) in neurointensive care focus on managing cerebral blood flow (CBF) and brain tissue oxygenation based on pressure signals. The decision support process relies on assumed relationships between cerebral perfusion pressure (CPP) and blood flow, pressure-flow relationships (PFRs), and shares this framework of assumptions with mathematical intracranial hemodynamics models. These foundational assumptions are difficult to verify, and their violation can impact clinical decision-making and model validity. Methods: A hypothesis- and model-driven method for verifying and understanding the foundational intracranial hemodynamic PFRs is developed and applied to a novel multi-modality monitoring dataset. Results: Model analysis of joint observations of CPP and CBF validates the standard PFR when autoregulatory processes are impaired as well as unmodelable cases dominated by autoregulation. However, it also identifies a dynamical regime -or behavior pattern-where the PFR assumptions are wrong in a precise, data-inferable way due to negative CPP-CBF coordination over long timescales. This regime is of both clinical and research interest: its dynamics are modelable under modified assumptions while its causal direction and mechanistic pathway remain unclear. Conclusion: Motivated by the understanding of mathematical physiology, the validity of the standard PFR can be assessed a) directly by analyzing pressure reactivity and mean flow indices (PRx and Mx) or b) indirectly through the relationship between CBF and other clinical observables. This approach could potentially help to personalize TBI care by considering intracranial pressure and CPP in relation to other data, particularly CBF. The analysis suggests a threshold using clinical indices of autoregulation jointly generalizes independently set indicators to assess CA functionality. These results support the use of increasingly data-rich environments to develop more robust hybrid physiological-machine learning models.

Brain tissue oxygen partial pressure monitoring and prognosis of patients with traumatic brain injury: a meta-analysis

To assess whether monitoring brain tissue oxygen partial pressure (PbtO2) or employing intracranial pressure (ICP)/cerebral perfusion pressure (CCP)-guided management improves patient outcomes, including mortality, hospital length of stay (LOS), mean daily ICP and mean daily CCP during the intensive care unit(ICU)stay. We searched the Web of Science, EMBASE, PubMed, Cochrane Library, and MEDLINE databases until December 12, 2023. Prospective randomized controlled and cohort studies were included. A meta-analysis was performed for the primary outcome measure, mortality, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Eleven studies with a total of 37,492 patients were included. The mortality in the group with PbtO2 was 29.0% (odds ratio: 0.73;95% confidence interval [CI]:0.56-0.96; P = 0.03; I = 55%), demonstrating a significant benefit. The overall hospital LOS was longer in the PbtO2 group than that in the ICP/CPP group (mean difference:2.03; 95% CI:1.03-3.02; P<0.0001; I = 39%). The mean daily ICP in the PbtO2 monitoring group was lower than that in the ICP/CPP group (mean difference:-1.93; 95% CI: -3.61 to -0.24; P = 0.03; I = 41%). Moreover, PbtO2 monitoring did not improve the mean daily CPP (mean difference:2.43; 95%CI: -1.39 to 6.25;P = 0.21; I = 56%).Compared with ICP/CPP monitoring, PbtO2 monitoring reduced the mortality and the mean daily ICP in patients with severe traumatic brain injury; however, no significant effect was noted on the mean daily CPP. In contrast, ICP/CPP monitoring alone was associated with a short hospital stay.

Intracranial pressure-flow relationships in traumatic brain injury patients expose gaps in the tenets of models and pressure-oriented management

Background

The protocols and therapeutic guidance established for treating traumatic brain injuries (TBI) in neurointensive care focus on managing cerebral blood flow (CBF) and brain tissue oxygenation based on pressure signals. The decision support process relies on assumed relationships between cerebral perfusion pressure (CPP) and blood flow, pressure-flow relationships (PFRs), and shares this framework of assumptions with mathematical intracranial hemodynamic models. These foundational assumptions are difficult to verify, and their violation can impact clinical decision-making and model validity.

Method

A hypothesis- and model-driven method for verifying and understanding the foundational intracranial hemodynamic PFRs is developed and applied to a novel multi-modality monitoring dataset.

Results

Model analysis of joint observations of CPP and CBF validates the standard PFR when autoregulatory processes are impaired as well as unmodelable cases dominated by autoregulation. However, it also identifies a dynamical regime -or behavior pattern- where the PFR assumptions are wrong in a precise, data-inferable way due to negative CPP-CBF coordination over long timescales. This regime is of both clinical and research interest: its dynamics are modelable under modified assumptions while its causal direction and mechanistic pathway remain unclear.

Conclusions

Motivated by the understanding of mathematical physiology, the validity of the standard PFR can be assessed a) directly by analyzing pressure reactivity and mean flow indices (PRx and Mx) or b) indirectly through the relationship between CBF and other clinical observables. This approach could potentially help personalize TBI care by considering intracranial pressure and CPP in relation to other data, particularly CBF. The analysis suggests a threshold using clinical indices of autoregulation jointly generalizes independently set indicators to assess CA functionality. These results support the use of increasingly data-rich environments to develop more robust hybrid physiological-machine learning models.

Intracranial Pressure and Brain Tissue Oxygen Multimodality Neuromonitoring in Gunshot Wounds to the Head in Children

OBJECTIVE

Gunshot wounds to the head (GSWH) are a cause of severe penetrating traumatic brain injury (TBI). Although multimodal neuromonitoring has been increasingly used in blunt pediatric TBI, its role in the pediatric population with GSWH is not known. We report on 3 patients who received multimodal neuromonitoring as part of clinical management at our institution and review the existing literature on pediatric GSWH.

METHODS

We identified 3 patients ≤18 years of age who were admitted to a quaternary children's hospital from 2005 to 2021 with GSWH and received invasive intracranial pressure (ICP) and Pbto2 (brain tissue oxygenation) monitoring with or without noninvasive near-infrared spectroscopy (NIRS). We analyzed clinical and demographic characteristics, imaging findings, and ICP, Pbto2, cerebral perfusion pressure, and rSo2 (regional cerebral oxygen saturation) NIRS trends.

RESULTS

All patients were male with an average admission Glasgow Coma Scale score of 4. One patient received additional NIRS monitoring. Episodes of intracranial hypertension (ICP ≥20 mm Hg) and brain tissue hypoxia (Pbto2 <15 mm Hg) or hyperemia (Pbto2 >35 mm Hg) frequently occurred independently of each other, requiring unique targeted treatments. rSo2 did not consistently mirror Pbto2. All children survived, with favorable Glasgow Outcome Scale-Extended score at 6 months after injury.

CONCLUSIONS

Use of ICP and Pbto2 multimodality neuromonitoring enabled specific management for intracranial hypertension or brain tissue hypoxia episodes that occurred independently of one another. Multimodality neuromonitoring has not been studied extensively in pediatric GSWH; however, its use may provide a more complete picture of patient injury and prognosis without significant added procedural risk.

The impact of brain tissue oxygenation monitoring on the Glasgow Outcome Scale/Glasgow Outcome Scale Extended in patients with moderate to severe traumatic brain injury: A systematic review

BACKGROUND

Traumatic brain injuries (TBIs) are one of the leading causes of death or long-term disability around the world. As a result of improvements in supportive care, patients are surviving more severe insults with more pronounced dependency on their families, hospitals, and long-term care facilities. The introduction of brain tissue oxygenation (PbtO2) monitoring aims to recognize episodes of reduced cerebral perfusion with and without associated increased intracranial pressure (ICP).

AIM

The aim of this review is to determine the impact of PbtO2 on the Glasgow Outcome Scale/Glasgow Outcome Scale Extended (GOS/GOSE) in patients with moderate to severe TBI.

DESIGN

Systematic review with narrative and meta-analysis. All original research in which adult patients undergoing PbtO2 were compared with a control group of traditional ICP/cerebral perfusion pressure (CPP) monitoring. Both randomized controlled trials and observational studies were included in this review.

METHODS

Databases were searched in September 2022. The primary outcome of the review was the impact of PbtO2 monitoring on GOS/GOSE, while secondary outcomes were mortality and length of stay (LOS) in the intensive care unit (ICU).

RESULTS

Seven studies with a combined number of 770 patients were included in the review. These patients were adults ≥16 years of age. Only two of the studies included found a statistically significant association between PbtO2 monitoring and improved long-term neurological outcomes in patients with TBI (p = .01, p < .01). A meta-analysis of the secondary outcomes identified an associated reduction of mortality in favour of the group treated with PbtO2 monitoring (p < .0001). Results from studies examining LOS in ICU have demonstrated an associated increase of LOS in ICU in patients treated with PbtO2-guided therapy.

CONCLUSION

From the studies included in this review, only two found a statistically significant association between PbtO2 monitoring and long-term outcomes. It is unclear whether PbtO2 goal-directed therapy has a positive impact on the long-term neurological functions and mortality of patients suffering from TBI. A multicentre randomized controlled trial may provide further evidence, but not necessarily conclusive.

RELEVANCE TO CLINICAL PRACTICE

Further research is warranted to determine the efficacy of the introduction of this new monitoring system to guide local policy change.

Brain Tissue Oxygenation-Guided Therapy and Outcome in Traumatic Brain Injury: A Single-Center Matched Cohort Study

Brain tissue oxygenation (PbtO2)-guided therapy can improve the neurological outcome of traumatic brain injury (TBI) patients. With several Phase-III ongoing studies, most of the existing evidence is based on before-after cohort studies and a phase-II randomized trial. The aim of this study was to assess the effectiveness of PbtO2-guided therapy in a single-center cohort. We performed a retrospective analysis of consecutive severe TBI patients admitted to our center who received either intracranial pressure (ICP) guided therapy (from January 2012 to February 2016) or ICP/PbtO2-guided therapy (February 2017 to December 2019). A genetic matching was performed based on covariates including demographics, comorbidities, and severity scores on admission. Intracranial hypertension (IH) was defined as ICP > 20 mmHg for at least 5 min. Brain hypoxia (BH) was defined as PbtO2 < 20 mmHg for at least 10 min. IH and BH were targeted by specific interventions. Mann−Whitney U and Fisher’s exact tests were used to assess differences between groups. A total of 35 patients were matched in both groups: significant differences in the occurrence of IH (ICP 85.7% vs. ICP/PbtO2 45.7%, p < 0.01), ICU length of stay [6 (3−13) vs. 16 (9−25) days, p < 0.01] and Glasgow Coma Scale at ICU discharge [10 (5−14) vs. 13 (11−15), p = 0.036] were found. No significant differences in ICU mortality and Glasgow Outcome Scales at 3 months were observed. This study suggests that the role of ICP/PbtO2-guided therapy should await further confirmation in well-conducted large phase III studies.

Integrative physiological assessment of cerebral hemodynamics and metabolism in acute ischemic stroke

Restoring perfusion to ischemic tissue is the primary goal of acute ischemic stroke care, yet only a small portion of patients receive reperfusion treatment. Since blood pressure (BP) is an important determinant of cerebral perfusion, effective BP management could facilitate reperfusion. But how BP should be managed in very early phase of ischemic stroke remains a contentious issue, due to the lack of clear evidence. Given the complex relationship between BP and cerebral blood flow (CBF)-termed cerebral autoregulation (CA)-bedside monitoring of cerebral perfusion and oxygenation could help guide BP management, thereby improve stroke patient outcome. The aim of INFOMATAS is to 'identify novel therapeutic targets for treatment and management in acute ischemic stroke'. In this review, we identify novel physiological parameters which could be used to guide BP management in acute stroke, and explore methodologies for monitoring them at the bedside. We outline the challenges in translating these potential prognostic markers into clinical use.

Optimal Cerebral Perfusion Pressure Guided by Brain Oxygen Pressure Measurement

Background: Although increasing cerebral perfusion pressure (CPP) is commonly accepted to improve brain tissue oxygen pressure (PbtO₂), it remains unclear whether recommended CPP targets (i. e., >60 mmHg) would result in adequate brain oxygenation in brain injured patients. The aim of this study was to identify the target of CPP associated with normal brain oxygenation.

Methods: Prospectively collected data including patients suffering from acute brain injury and monitored with PbtO₂, in whom daily CPP challenge using vasopressors was performed. Initial CPP target was >60 mmHg; norepinephrine infusion was modified to have an increase in CPP of at least 10 mmHg at two different steps above the baseline values. Whenever possible, the same CPP challenge was performed for the following days, for a maximum of 5 days. CPP “responders” were patients with a relative increase in PbtO₂ from baseline values > 20%.

Results: A total of 53 patients were included. On the first day of assessment, CPP was progressively increased from 73 (70–76) to 83 (80–86), and 92 (90–96) mmHg, which resulted into a significant PbtO₂ increase [from 20 (17–23) mmHg to 22 (20–24) mmHg and 24 (22–26) mmHg, respectively; p < 0.001]. Median CPP value corresponding to PbtO₂ values > 20 mmHg was 79 (74–87) mmHg, with 2 (4%) patients who never achieved such target. Similar results of CPP targets were observed the following days. A total of 25 (47%) were PbtO₂ responders during the CPP challenge on day 1, in particular if low PbtO₂ was observed at baseline.

Conclusions: PbtO₂ monitoring can be an effective way to individualize CPP values to avoid tissue hypoxia. Low PbtO₂ values at baseline can identify the responders to the CPP challenge.

Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy

The brain tissue partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO₂ neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO₂ with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO₂ and NIRS neuromonitoring is given.

Thirty-day clinical outcome of traumatic brain injury patients with acute extradural and subdural hematoma: a cohort study at Mulago National Referral Hospital, Uganda

Background

Increasing traumatic brain injury (TBI) has paralleled the need for decompression surgery for acute subdural (ASDH) and acute extradural haematoma (AEDH). Knowledge of key determinants of clinical outcomes of such patients is mandatory to guide treatment protocols.

Objective

To determine the 30-day clinical outcomes and predictor variables for patients with extra-axial hematomas at Mulago National Referral Hospital in Uganda.

Methods

Prospective observational cohort study of 109 patients with computed tomography (CT) confirmed extra-axial hematomas. Ethical clearance was obtained from the School of Medicine Research and Ethics Committee of College of Health Sciences, Makerere University (REC REF. 2018-185). Admitted patients were followed-up and reassessed for Glasgow Outcome Scale (GOS) and final disposition. Multivariate regression analysis was performed using Stata 14.0 (StataCorp. 2015) at 95% confidence interval, regarding p < 0.05 as statistically significant.

Results

The overall proportion of favorable outcome was 71.7% (n = 71), with 42.3% (n = 11) and 81.7% (n = 58) for ASDH and AEDH, respectively (p = 0.111). Factors associated with a favorable outcome were admission systolic BP > 90 mmHg [IRR = 0.88 (0.26–0.94) 95%CI, p = 0.032), oxygen saturation > 90% [IRR = 0.5 (0.26–0.94) 95%CI, p = 0.030] and diagnosis AEDH [IRR = 0.53 (0.30–0.92) 95%CI, p = 0.025). Moderate TBI [IRR = 4.57 (1.15–18.06) 95%CI, p = 0.03] and severe TBI [IRR = 6.79 (2.32–19.86) 95%CI, p < 0.001] were significantly associated with unfavorable outcomes.

Conclusion

The study revealed that post resuscitation GCS, systolic BP, oxygen circulation, and diagnosis of AEDH at admission are the most important determinants of outcome for patients with extra-axial intracranial hematomas. These findings are valuable for the triaging teams in resource-constrained settings.

Children With Severe Traumatic Brain Injury, Intracranial Pressure, Cerebral Perfusion Pressure, What Does it Mean? A Review of the Literature

Severe traumatic brain injury is a leading cause of morbidity and mortality in children. In 2003 the Brain Trauma Foundation released guidelines that have since been updated (2010) and have helped standardize and improve care. One area of care that remains controversial is whether the placement of an intracranial pressure monitor is advantageous in the management of traumatic brain injury. Another aspect of care that is widely debated is whether management after traumatic brain injury should be based on intracranial pressure-directed therapy, cerebral perfusion pressure-directed therapy, or a combination of the two. The aim of this article was to provide an overview and review the current evidence regarding these questions.

Intensive Care in Traumatic Brain Injury Including Multi-Modal Monitoring and Neuroprotection

Moderate to severe traumatic brain injuries (TBI) require treatment in an intensive care unit (ICU) in close collaboration of a multidisciplinary team consisting of different medical specialists such as intensivists, neurosurgeons, neurologists, as well as ICU nurses, physiotherapists, and ergo-/logotherapists. Major goals include all measurements to prevent secondary brain injury due to secondary brain insults and to optimize frame conditions for recovery and early rehabilitation. The distinction between moderate and severe is frequently done based on the Glascow Coma Scale and therefore often is just a snapshot at the early time of assessment. Due to its pathophysiological pathways, an initially as moderate classified TBI may need the same sophisticated surveillance, monitoring, and treatment as a severe form or might even progress to a severe and difficult to treat affection. As traumatic brain injury is rather a syndrome comprising a range of different affections to the brain and as, e.g., age-related comorbidities and treatments additionally may have a great impact, individual and tailored treatment approaches based on monitoring and findings in imaging and respecting pre-injury comorbidities and their therapies are warranted.

Cerebral metabolism is not affected by moderate hyperventilation in patients with traumatic brain injury

Background

Hyperventilation-induced hypocapnia (HV) reduces elevated intracranial pressure (ICP), a dangerous and potentially fatal complication of traumatic brain injury (TBI). HV decreases the arteriolar diameter of intracranial vessels, raising the risk of cerebral ischemia. The aim of this study was to characterize the effects of moderate short-term HV in patients with severe TBI by using concomitant monitoring of cerebral metabolism, brain tissue oxygen tension (PbrO₂), and cerebral hemodynamics with transcranial color-coded duplex sonography (TCCD).

Methods

This prospective trial was conducted between May 2014 and May 2017 in the surgical intensive care unit (ICU) at the University Hospital of Zurich. Patients with nonpenetrating TBI older than 18 years of age with a Glasgow Coma Scale (GCS) score < 9 at presentation and with ICP monitoring, PbrO₂, and/or microdialysis (MD) probes during ICU admission within 36 h after injury were included in our study. Data collection and TCCD measurements were performed at baseline (A), at the beginning of moderate HV (C), after 50 min of moderate HV (D), and after return to baseline (E). Moderate HV was defined as arterial partial pressure of carbon dioxide 4–4.7 kPa. Repeated measures analysis of variance was used to compare variables at the different time points, followed by post hoc analysis with Bonferroni adjustment as appropriate.

Results

Eleven patients (64% males, mean age 36 ± 14 years) with an initial median GCS score of 7 (IQR 3–8) were enrolled. During HV, ICP and mean flow velocity (CBFV) in the middle cerebral artery decreased significantly. Glucose, lactate, and pyruvate in the brain extracellular fluid did not change significantly, whereas PbrO₂ showed a statistically significant reduction but remained within the normal range.

Conclusion

Moderate short-term hyperventilation has a potent effect on the cerebral blood flow, as shown by TCCD, with a concomitant ICP reduction. Under the specific conditions of this study, this degree of hyperventilation did not induce pathological alterations of brain metabolites and oxygenation.

Trial registration

NCT03822026. Registered on 30 January 2019.

Intracranial mechanisms for preserving brain blood flow in health and disease

The brain is an exceptionally energetically demanding organ with little metabolic reserve, and multiple systems operate to protect and preserve the brain blood supply. But how does the brain sense its own perfusion? In this review, we discuss how the brain may harness the cardiovascular system to counter threats to cerebral perfusion sensed via intracranial pressure (ICP), cerebral oxygenation and ischaemia. Since the work of Cushing over 100 years ago, the existence of brain baroreceptors capable of eliciting increases in sympathetic outflow and blood pressure has been hypothesized. In the clinic, this response has generally been thought to occur only in extremis, to perfuse the severely ischaemic brain as cerebral autoregulation fails. We review evidence that pressor responses may also occur with smaller, physiologically relevant increases in ICP. The incoming brain oxygen supply is closely monitored by the carotid chemoreceptors; however, hypoxia and other markers of ischaemia are also sensed intrinsically by astrocytes or other support cells within brain tissue itself and elicit reactive hyperaemia. Recent studies suggest that astrocytic oxygen signalling within the brainstem may directly affect sympathetic nerve activity and blood pressure. We speculate that local cerebral oxygen tension is a major determinant of the mean level of arterial pressure and discuss recent evidence that this may be the case. We conclude that intrinsic intra- and extra-cranial mechanisms sense and integrate information about hypoxia/ischaemia and ICP and play a major role in determining the long-term level of sympathetic outflow and arterial pressure, to optimize cerebral perfusion.

Brain Multimodality Monitoring: Updated Perspectives

The challenges posed by acute brain injury (ABI) involve the management of the initial insult in addition to downstream inflammation, edema, and ischemia that can result in secondary brain injury (SBI). SBI is often subclinical, but can be detected through physiologic changes. These changes serve as a surrogate for tissue injury/cell death and are captured by parameters measured by various monitors that measure intracranial pressure (ICP), cerebral blood flow (CBF), brain tissue oxygenation (PbtO2), cerebral metabolism, and electrocortical activity. In the ideal setting, multimodality monitoring (MMM) integrates these neurological monitoring parameters with traditional hemodynamic monitoring and the physical exam, presenting the information needed to clinicians who can intervene before irreversible damage occurs. There are now consensus guidelines on the utilization of MMM, and there continue to be new advances and questions regarding its use. In this review, we examine these recommendations, recent evidence for MMM, and future directions for MMM.

Monitoring of brain and systemic oxygenation in neurocritical care patients

Maintenance of adequate oxygenation is a mainstay of intensive care, however, recommendations on the safety, accuracy, and the potential clinical utility of invasive and non-invasive tools to monitor brain and systemic oxygenation in neurocritical care are lacking. A literature search was conducted for English language articles describing bedside brain and systemic oxygen monitoring in neurocritical care patients from 1980 to August 2013. Imaging techniques e.g., PET are not considered. A total of 281 studies were included, the majority described patients with traumatic brain injury (TBI). All tools for oxygen monitoring are safe. Parenchymal brain oxygen (PbtO2) monitoring is accurate to detect brain hypoxia, and it is recommended to titrate individual targets of cerebral perfusion pressure (CPP), ventilator parameters (PaCO2, PaO2), and transfusion, and to manage intracranial hypertension, in combination with ICP monitoring. SjvO2 is less accurate than PbtO2. Given limited data, NIRS is not recommended at present for adult patients who require neurocritical care. Systemic monitoring of oxygen (PaO2, SaO2, SpO2) and CO2 (PaCO2, end-tidal CO2) is recommended in patients who require neurocritical care.

Options for managing raised intracranial pressure

This article reviews the current monitoring and management options for raised intracranial pressure (ICP), primarily in traumatic head injuries, in line with current literature and guidelines. The use of ICP monitoring is useful in managing, predicting outcomes, following the progression and guiding interventions of neurological disease states.

Patients with raised ICP should be monitored closely in a neurocritical care setting where appropriate interventions can be instituted based on available monitoring parameters. Various first- and second-tier methods should be considered, with the primary goal to decrease secondary insult to brain tissue for best outcomes.

Variations of the blood gas levels and thermodilutional parameters during ICP monitoring after severe head trauma in children

PURPOSE

The purpose of this study was to define, in children following head trauma and GSC ≤ 8, at which level of intracranial pressure (ICP), the thermodilutional, and gas analytic parameters implicated in secondary cerebral insults shows initial changes.

METHODS

We enrolled in the study 56 patients: 30 males and 26 females, mean age 71 ± 52 months. In all children, volumetric hemodynamic and blood gas parameters were monitored following initial resuscitation and every 4 h thereafter or whenever a hemodynamic deterioration was suspected. During the cumulative hospital stay, a total of 1050 sets of measurements were done. All parameters were stratified in seven groups according to ICP (group A1 = 0-5 mmHg, group A2 = 6-10 mmHg, group A3 = 11-15 mmHg, group A4 16-20 mmHg, group A5 21-25 mmHg, group A6 26-30 mmHg, group A7 >31 mmHg).

RESULTS

Mean values of jugular oxygen saturation (SJO2), jugular oxygen partial pressure (PJO2), extravascular lung water (EVLWi), pulmonary vascular permeability (PVPi), fluid overload (FO), and cerebral extraction of oxygen (CEO2) vary significantly from A3 (11-15 mmHg) to A4 (16-20 mmHg). They relate to ICP in a four-parameter sigmoidal function (4PS function with: r(2) = 0.90), inflection point of 15 mmHg of ICP, and a maximum curvature point on the left horizontal asymptote at 13 mmHg of ICP.

CONCLUSIONS

Mean values of SJO2, PJO2, EVLWi, PVPi, FO, and CEO2 become pathologic at 15 mmHg of ICP; however, the curve turns steeper at 13 mmHg, possibly a warning level in children for the development of post head trauma secondary insult.

Accuracy of brain multimodal monitoring to detect cerebral hypoperfusion after traumatic brain injury*

OBJECTIVE

To examine the accuracy of brain multimodal monitoring-consisting of intracranial pressure, brain tissue PO2, and cerebral microdialysis--in detecting cerebral hypoperfusion in patients with severe traumatic brain injury.

DESIGN

Prospective single-center study.

PATIENTS

Patients with severe traumatic brain injury.

SETTING

Medico-surgical ICU, university hospital.

INTERVENTION

Intracranial pressure, brain tissue PO2, and cerebral microdialysis monitoring (right frontal lobe, apparently normal tissue) combined with cerebral blood flow measurements using perfusion CT.

MEASUREMENTS AND MAIN RESULTS

Cerebral blood flow was measured using perfusion CT in tissue area around intracranial monitoring (regional cerebral blood flow) and in bilateral supra-ventricular brain areas (global cerebral blood flow) and was matched to cerebral physiologic variables. The accuracy of intracranial monitoring to predict cerebral hypoperfusion (defined as an oligemic regional cerebral blood flow < 35 mL/100 g/min) was examined using area under the receiver-operating characteristic curves. Thirty perfusion CT scans (median, 27 hr [interquartile range, 20-45] after traumatic brain injury) were performed on 27 patients (age, 39 yr [24-54 yr]; Glasgow Coma Scale, 7 [6-8]; 24/27 [89%] with diffuse injury). Regional cerebral blood flow correlated significantly with global cerebral blood flow (Pearson r = 0.70, p < 0.01). Compared with normal regional cerebral blood flow (n = 16), low regional cerebral blood flow (n = 14) measurements had a higher proportion of samples with intracranial pressure more than 20 mm Hg (13% vs 30%), brain tissue PO2 less than 20 mm Hg (9% vs 20%), cerebral microdialysis glucose less than 1 mmol/L (22% vs 57%), and lactate/pyruvate ratio more than 40 (4% vs 14%; all p < 0.05). Compared with intracranial pressure monitoring alone (area under the receiver-operating characteristic curve, 0.74 [95% CI, 0.61-0.87]), monitoring intracranial pressure + brain tissue PO2 (area under the receiver-operating characteristic curve, 0.84 [0.74-0.93]) or intracranial pressure + brain tissue PO2+ cerebral microdialysis (area under the receiver-operating characteristic curve, 0.88 [0.79-0.96]) was significantly more accurate in predicting low regional cerebral blood flow (both p < 0.05).

CONCLUSION

Brain multimodal monitoring-including intracranial pressure, brain tissue PO2, and cerebral microdialysis--is more accurate than intracranial pressure monitoring alone in detecting cerebral hypoperfusion at the bedside in patients with severe traumatic brain injury and predominantly diffuse injury.

Current concepts of optimal cerebral perfusion pressure in traumatic brain injury

Traumatic brain injury (TBI) consists of varied pathophysiological consequences and alteration of intracranial dynamics, reduction of the cerebral blood flow and oxygenation. In the past decade more emphasis has been directed towards optimizing cerebral perfusion pressure (CPP) in patients who have suffered TBI. Injured brain may show signs of ischemia if CPP remains below 50 mmHg and raising the CPP above 60 mmHg may avoid cerebral oxygen desaturation. Though CPP above 70 mmHg is influential in achieving an improved patient outcome, maintenance of CPP higher than 70 mmHg was associated with greater risk of acute respiratory distress syndrome (ARDS). The target CPP has been laid within 50-70 mmHg. Cerebral blood flow and metabolism are heterogeneous after TBI and with regional temporal differences in the requirement for CPP. Brain monitoring techniques such as jugular venous oximetry, monitoring of brain tissue oxygen tension (PbrO₂), and cerebral microdialysis provide complementary and specific information that permits the selection of the optimal CPP. This review highlights the rationale for use CPP directed therapies and neuromonitoring to identify optimal CPP of head injured patients. The article also reviews the evidence provided by various clinical trials regarding optimal CPP and their application in the management of head injured patients.

Monitoring of acute traumatic brain injury in adults to prevent secondary brain damage

ABSTRACT: Traumatic brain injury is typically characterized by the primary injury initiating a cascade of pathologic changes that then lead to secondary brain injury. Secondary brain injury is amenable to different therapeutic options. Monitoring of otherwise occult pathologic changes involving oxygenation and metabolism is crucial for treatment decisions. Currently, decision-making is mainly based on measuring intracranial pressure and cerebral perfusion pressure. Importantly, extending neuromonitoring by including parameters reflecting cerebral perfusion, oxygenation and metabolism may improve treatment of traumatic brain injury patients by detecting neuronal damage despite optimal intracranial pressure or cerebral perfusion pressure and preventing unnecessarily aggressive treatment potentially causing local and systemic harm. In this review, the authors describe the advantages and disadvantages of contemporary, extended neuromonitoring methods in traumatic brain injury patients aimed at unmasking secondary brain damage as early as possible.

Traumatic Brain Injury pathophysiology and treatments: early, intermediate, and late phases post-injury

Traumatic Brain Injury (TBI) affects a large proportion and extensive array of individuals in the population. While precise pathological mechanisms are lacking, the growing base of knowledge concerning TBI has put increased emphasis on its understanding and treatment. Most treatments of TBI are aimed at ameliorating secondary insults arising from the injury; these insults can be characterized with respect to time post-injury, including early, intermediate, and late pathological changes. Early pathological responses are due to energy depletion and cell death secondary to excitotoxicity, the intermediate phase is characterized by neuroinflammation and the late stage by increased susceptibility to seizures and epilepsy. Current treatments of TBI have been tailored to these distinct pathological stages with some overlap. Many prophylactic, pharmacologic, and surgical treatments are used post-TBI to halt the progression of these pathologic reactions. In the present review, we discuss the mechanisms of the pathological hallmarks of TBI and both current and novel treatments which target the respective pathways.

Parenchymal brain oxygen monitoring in the neurocritical care unit

Patients admitted to the neurocritical care unit (NCCU) often have serious conditions that can be associated with high morbidity and mortality. Pharmacologic agents or neuroprotectants have disappointed in the clinical environment. Current NCCU management therefore is directed toward identification, prevention, and treatment of secondary cerebral insults that evolve over time and are known to aggravate outcome. This strategy is based on a variety of monitoring techniques including use of intraparenchymal monitors. This article reviews parenchymal brain oxygen monitors, including the available technologies, practical aspects of use, the physiologic rationale behind their use, and patient management based on brain oxygen.

Moderate and severe traumatic brain injury: pathophysiology and management

Traumatic brain injury (TBI) is a serious disorder that is all too common. TBI ranges in severity from mild concussion to a severe life-threatening state. Across this spectrum, rational therapeutic approaches exist. Early identification that TBI has occurred in a patient is paramount to optimal outcome. Proper clinical management should be instituted as soon as possible by appropriately trained medical providers. More seriously injured patients must be triaged to advanced care centers. It is only through this rational approach to TBI that patients may expect to achieve optimal clinical and functional outcome.